1. Field of the Invention
This invention relates, generally, to active element-containing devices Chat are disposed below ground level when not in use and that are positioned above ground when in use.
2. Description of the Prior Art
U.S. Pat. No. 4,974,134 to the present inventor shows a light-containing housing telescopically received within a main housing that is disposed in a vertical bore formed in the ground. A slidably mounted motor positioned in a motor housing drives the light housing out of the main body when lighting is desired and retracts the light housing into the main body when it is not. The top of the light housing is substantially flush with the ground when said light housing is fully retracted.
In that early design, the motor is switched on and off by switches that are longitudinally spaced from one another in the motor housing, i.e., a first limit switch is disposed near the upper end of the motor housing and a second limit switch is positioned near the lower end of said housing. The output shaft of the motor rotates in a first direction to drive the light housing upwardly; as long as the light housing is traveling upwardly, the position of the motor is fixed. However, when the light housing is fully deployed, continued operation of the motor drives the motor downwardly, towards the bottom of the motor housing. A contact on the motor then connects with a contact on the upper limit switch, and the motor is deactivated. Conversely, when the output shaft of the motor is rotating in an opposite direction to retract the light housing, the motor is centered in the motor housing until the light housing is fully retracted. Continued operation of the motor then pulls the motor towards the top of the motor housing, until a contact on the motor abuts a contact on the lower limit switch that deactivates the motor.
Thus, the motor travels in a longitudinal direction within the motor housing; this requires that the housing be elongate. Moreover, the bearing that seals the output shaft of the motor must not only handle the rotational aspect of said output shaft, but it must also handle the longitudinal displacement aspect as well, i.e., the bearing must seal in different ways.
What is needed, then, is a design that makes less demand on the seal so that a less expensive seal could be used. Moreover, a design that would shorten the length of the motor housing would be desirable because less materials would then be required to fabricate the housing and the bore in the earth would not need to be quite as deep. Moreover, a simpler way to achieve motor activation and deactivation, and reversal of output shaft rotational direction, would make the apparatus less expensive to manufacture and perhaps more reliable as well. However, at the time the present invention was made, neither the just-described earlier device nor other known devices in the field of this invention taught or suggested to those of ordinary skill in this art how such art could be advanced in a significant way.